The use of wireless communication devices such as telephones, pagers, personal digital assistants, laptop computers, etc., hereinafter referred to collectively as “mobile appliances” or “mobiles stations” has become prevalent in today's society. In recent years, at the urging of public safety groups, there has been increased interest in technology which can determine the geographic position or “geo-locate” a mobile station in certain circumstances.
Estimating the location of a mobile station may require one or more types of calibration data associated with the mobile station (e.g., signal strength, round trip time, time difference of arrival (TDOA), ground truth data, etc.). Determining precise ground truth measurements is important when generating an accurate calibration database. Without accurate ground truth information, the calibration database will contain significant errors which will in turn be reflected by poor location estimates. Any device used to retrieve ground truth data may produce some degree of signal degradation or drop-out. In the case of a GPS receiver used to collect ground truth data, degradation or drop-out could occur, for example, due to poor satellite visibility or high dilution of precision (DOP).
Referring to FIG. 1, a vehicle 40 may be configured with a collection device 45 to collect calibration data. Once calibration data has been obtained, it may be stored locally in an internal memory of the collection device 45, or the data may be transmitted to a receiving base station 60, where the data is stored in a calibration database 50.
The vehicle 40 may include a dead-reckoning device (not shown) to collect data during periods of signal degradation or drop-out. Such devices attempt to calculate the location of the vehicle when GPS location signaling obtained from a GPS satellite 70 becomes unavailable. Dead reckoning operates by estimating a location of a moving vehicle 40 using information, such as, but not limited to, the last accurate GPS location, velocity of the vehicle 40 and may include other known information.
Dead reckoning schemes often produce data results that may be unsatisfactory when attempting to perform a location estimate. FIG. 2 illustrates an exemplary dead reckoning operation. Referring to FIG. 2, a vehicle's estimated position is illustrated by the line (T) along the street. During a dead reckoning operation, there may be an increased chance of location error and the vehicle's estimated position (T) may be erroneous with respect to the actual position of the vehicle.
Current collection procedures utilized to generate a calibration database 50 may also be laborious, time-consuming and expensive. Simplifying the test and measurement equipment (T&M) needed, and the procedures for obtaining calibration data may save time and expenses.